1. Field of the Invention
The present invention relates to a semiconductive rubber member that is used as a developing roller, a cleaning roller, a charging roller, a transfer roller, and the like mounted on an electrophotographic apparatus. More particularly, the present invention relates to a semiconductive rubber member which can be used preferably as the developing roller for attaching an nonmagnetic one-component toner to a photoreceptor by imparting a high charging property to the nonmagnetic one-component toner. The developing roller is used in an image-forming mechanism of an electrophotographic apparatus such as a laser beam printer and the like.
2. Description of the Related Art
In recent years, regarding an electrophotographic apparatus such as a laser printer, research has been widely made to realize a high-speed operation and form a high-quality image. To cope with the situation, polymerized toner that is spherical and can be reduced in the diameter thereof has come to be widely used.
As the polymerized toner, a one-component toner not using a carrier has come to be widely used instead of a two-component toner, composed of a carrier consisting of ferrite powder or iron powder and a toner, which has been hitherto used because it is easy to design on the mixing of the carrier and the toner. In such a situation, as the developing roller which receives toner and supplies it faithfully to a toner image formed on the photoreceptor, magnetic type which has been mainly used is being replaced with a semiconductive elastic rubber roller.
When the two-component toner using the carrier is used, it is easy to transport the toner to the photoreceptor owing to electrical and magnetic actions. But when the one-component toner is used, the magnetic action cannot be utilized to transport the toner. Therefore it is necessary to uniformly form the surface of the developing roller which is the end surface of an electrode. Further to uniformly attach the toner, the particle diameter of which is of a micron order to the photoreceptor, it is necessary that the electrical properties represented by an resistance value is uniform inside the developing roller so that when a bias electric potential is applied to the developing roller, a uniform electric potential distribution is obtained.
Because the one-component toner does not contain the carrier, the developing roller is required to have the function of controlling the charging property of the toner. That is, the developing roller is required to impart charging property to the toner and maintain the charging property imparted to the toner. When the charged amount of the toner is insufficient, an electrostatic force is insufficient and hence the toner is not transported to the electrostatic latent image formed on the photoreceptor. Consequently owing to the rotation of the developing roller, there occur a change in density, generation of a ghost image, photographic fog, and the like.
To comply with the above-described demands, various developing rollers are proposed. For example, disclosed in Japanese Patent Application Laid-Open No. 2002-194203 (patent document 1) is the rubber member, for electrophotographic use, made of the rubber material containing the ionic-conductive epichlorohydrin rubber and the calcium carbonate, whose particle diameter is restricted to a specific diameter, which is dispersed in the epichlorohydrin rubber. In the rubber member, the electric resistance of the rubber member is controlled not electronically because a conductive filler is not used but by ionic conduction to improve uniformity and enhance processing accuracy by using the filler. But the performance for charging toner and the durability of the electric charge imparted thereto are not high. Thus when the rubber member is used as the developing roller, it does not provide a high-quality image.
In the disclosure made in Japanese Patent Application Laid-Open No. 2001-357735 (patent document 2), to control the performance for charging toner, the surface of the conductive member is coated with the treating agent containing the amine compound. A very high dimensional accuracy is demanded for the developing roller. Thus a specific apparatus is required to treat the surface of the conductive member with high accuracy. Further the yield is very low, which leads to an increase of the manufacturing cost. In addition, because the material of the conductive member and the material of the coating agent are different from each other, the coating agent will separate from the surface of the conductive member when the conductive member is manufactured or when it is used.
As described above, to impart a high charging property to the unmagnetic one-component toner, the developing roller is required to have the performance of applying an electrical charge to the toner and maintaining the applied electrical charge. When a coating layer is formed on the surface of rubber layer, the cost for manufacturing the developing roller is high. Therefore it is difficult to form the coating layer. Even if the coating layer is formed on the surface of rubber layer, it may separate therefrom.
Patent document 1: Japanese Patent Application Laid-Open No. 2002-194203
Patent document 2: Japanese Patent Application Laid-Open No. 2001-357735